Fuel Cell Separators

Abstract

The disclosure relates to fuel cell systems including a multiplicity of unit fuel cells arranged in a stack, with each unit fuel cell separated by an electrode separator assembly. Each unit fuel cell includes a membrane electrode assembly with an anode, a cathode, and a solid polymer electrolyte membrane disposed between the anode and the cathode. An anode separator is positioned between each membrane electrode assembly of adjoining unit fuel cells within the stack in contact with an anode, and a cathode separator is positioned between each membrane electrode assembly of adjoining unit fuel cells within the stack in contact with a cathode. A surface of an anode separator is joined to a surface of a cathode separator of an adjoining unit fuel cell to form an electrode separator assembly. The disclosure also relates to a method of making a fuel cell assembly.

1 . A fuel cell system, comprising:
 a plurality of unit fuel cells arranged in a stack of adjoining unit fuel cells, each unit fuel cell comprising a membrane electrode assembly including an anode, a cathode, and a solid polymer electrolyte membrane disposed between the anode and the cathode;   an anode separator positioned between each unit fuel cell in contact with the anode of the membrane electrode assembly of each unit fuel cell within the stack; and   a cathode separator positioned between each unit fuel cell in contact with the cathode for the membrane electrode assembly of each adjoining unit fuel cell within the stack;   wherein a surface of the anode separator for each unit fuel cell is joined to a surface of the cathode separator for each adjoining unit fuel cell to form an electrode separator assembly.   
   
   
       2 . The fuel cell system of  claim 1 , wherein the fuel cell stack is held together by a plurality of connecting members, wherein each connecting member extends through each electrode separator assembly and each membrane electrode assembly without penetrating an activating surface of an anode, a cathode, or a solid polymer electrolyte membrane. 
   
   
       3 . The fuel cell system of  claim 2 , further comprising one or more end plates positioned at an end of the fuel cell stack in contact with one of a cathode separator or anode separator, wherein each connecting member extends through a bolt hole formed through a contact surface between each electrode separator assembly, membrane electrode assembly, and end plate. 
   
   
       4 . The fuel cell system of  claim 1 , wherein each anode separator is joined to each adjoining cathode separator by a plurality of joints formed between one or more of the contact surfaces between the anode separator and the adjoining cathode separator. 
   
   
       5 . The fuel cell system of  claim 4 , wherein each of the cathode separator, cathode, solid polymer electrolyte membrane, anode, and anode separator for each unit fuel cell comprise edges surrounding the contact surfaces, the edges forming a generally rectangular peripheral edge perimeter for each unit fuel cell. 
   
   
       6 . The fuel cell system of  claim 5 , wherein an edge of each unit fuel cell is joined to an edge of the adjoining unit fuel cell and held together by at least one connecting member extending through the fuel cell stack at a position proximate each edge. 
   
   
       7 . The fuel cell system of  claim 5 , wherein the number of joints positioned on a contact surface of each anode separator with the adjoining anode decreases from a position proximate a center of the contact surface with respect to the peripheral edge perimeter, to a position proximate the peripheral edge perimeter of each unit fuel cell. 
   
   
       8 . The fuel cell system of  claim 7 , wherein each anode separator is joined to the adjoining cathode separator by at least one joint positioned proximate the center of the contact surface of each anode separator. 
   
   
       9 . The fuel cell system of  claim 1 , wherein the anode separators and cathode separators comprise a metal, and wherein each anode separator is joined to each cathode separator of the adjoining unit fuel cell by one or more welds. 
   
   
       10 . The fuel cell system of  claim 9 , wherein the unit fuel cells within the fuel cell stack each comprise a plurality of edges defining an outer perimeter for each unit fuel cell, and wherein a weld may be formed between each anode separator and each adjoining cathode separator proximate an edge of each unit fuel cell. 
   
   
       11 . The fuel cell system of  claim 9 , further comprising a plurality of welds between each anode separator and each adjoining cathode separator, wherein the welds are positioned proximate to a contact surface of each anode separator with each adjoining cathode separator. 
   
   
       12 . The fuel cell system of  claim 9 , wherein the welds are positioned proximate a gas flow channel formed between the anode separator and the cathode separator; wherein the gas flow channel defines a region of low gas moisture content and a region of high gas moisture content region; and wherein the weld density is lower in the high gas moisture content region than in the low gas moisture content region. 
   
   
       13 . The fuel cell system of  claim 12 , wherein the high gas moisture content region comprises a first region between a first face of the anode separator and a first face of an adjoining cathode separator; and wherein the low gas moisture content region comprises a second region between a second face of the anode separator on a side opposite to the first face of the anode separator and a second face of the adjoining cathode separator on a side opposite to the first face of the adjoining cathode separator; and wherein the weld density is higher in the second region than in the first region. 
   
   
       14 . The fuel cell system of  claim 12 , wherein the gas flow channel defines a fuel gas exit on a surface of the anode separator, and wherein the weld density is lower proximate the fuel gas exit than in other areas on the surface of the anode separator. 
   
   
       15 . The fuel cell system of  claim 12 , wherein the gas flow channel defines an oxidant gas exit on a surface of the cathode separator, and wherein the weld density is lower proximate the oxidant gas exit than in other areas on the surface of the cathode separator. 
   
   
       16 . The fuel cell system of  claim 1 , wherein each cathode separator comprises a plurality of grooves formed on a surface of the separator in contact with a surface of the adjoining cathode. 
   
   
       17 . The fuel cell system of  claim 16 , wherein the grooves are arranged in a generally serpentine path forming a fluid direction channel on the surface of each cathode separator. 
   
   
       18 . The fuel cell system of  claim 1 , wherein each anode separator is joined to the cathode separator of each adjoining unit fuel cell to form a fluid conduit between each anode separator and each cathode separator of each adjoining unit fuel cell. 
   
   
       19 . The fuel cell system of  claim 18 , wherein each anode separator is joined to the cathode separator of each adjoining unit fuel cell by a plurality of welds. 
   
   
       20 . The fuel cell system of  claim 18 , wherein the fluid conduit contains a fuel cell working fluid. 
   
   
       21 . The fuel cell system of  claim 20 , wherein the fuel cell working fluid is selected from the group consisting of a fuel gas, an oxidant gas, and water. 
   
   
       22 . A fuel cell assembly, comprising:
 a plurality of unit fuel cells arranged in a fuel cell stack, each unit fuel cell comprising a membrane electrode assembly including an anode, a cathode, and an electrolyte membrane disposed between the anode and the cathode; and   means for joining each cathode to each anode, thereby electrically connecting each cathode to each anode and providing a delivery path for at least one fuel cell working fluid to each cathode and each anode.   
   
   
       23 . The fuel cell assembly of  claim 22  wherein the fuel cell working fluid is one or more of the group consisting of a fuel gas, an oxidant gas, and water. 
   
   
       24 . A method of making a fuel cell assembly, comprising:
 forming a fuel cell stack by stacking a plurality of unit fuel cells, each unit fuel cell comprising a membrane electrode assembly including an anode in contact with an anode separator, a cathode in contact with a cathode separator, and a solid polymer electrolyte membrane disposed between the anode and the cathode; and   joining each anode separator to an adjoining cathode separator of the adjoining unit fuel cell.   
   
   
       25 . The method of  claim 24 , wherein joining is achieved by welding a contact surface of each anode separator to a contact surface of the adjoining cathode separator. 
   
   
       26 . The method of  claim 25 , wherein welding is selected from laser beam or electron beam welding.